Energy adaptive communication for medical devices

ABSTRACT

System and methods for energy adaptive communications between medical devices are disclosed. In one example, a medical device includes a communication module configured to deliver a plurality of pulses to tissue of a patient, where each pulse has an amount of energy. A control module operatively coupled to the communication module, may be configured to, for each delivered pulse, determine whether the delivered pulse produces an unwanted stimulation of the patient and to change the amount of energy of the plurality of pulses over time so as to identify an amount of energy that corresponds to an unwanted stimulation threshold for the pulses. The control module may then set a maximum energy value for communication pulses that is below the unwanted stimulation threshold, and may deliver communication pulses below the maximum energy value during communication with another medical device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S.Provisional Application Ser. No. 62/043,123, filed Aug. 28, 2014, theentirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to systems, devices, andmethods for communicating information, and more particularly, tosystems, devices, and methods for communicating information betweenmedical devices in a power efficient manner.

BACKGROUND

Implantable medical devices are commonly used today to monitor a patientand/or deliver therapy to a patient. For example, implantable sensorsare often used to monitor one or more physiological parameters of apatient, such as heart beats, heart sounds, ECG, respiration, etc. Inanother example, implantable neurostimulators can be used to provideneurostimulation therapy to a patient. In yet another example, pacingdevices can be used to treat patients suffering from various heartconditions that may result in a reduced ability of the heart to deliversufficient amounts of blood to a patient's body. Such heart conditionsmay lead to rapid, irregular, and/or inefficient heart contractions. Tohelp alleviate some of these conditions, various devices (e.g.,pacemakers, defibrillators, etc.) are often implanted in a patient'sbody. Such devices may monitor and provide electrical stimulation to theheart to help the heart operate in a more normal, efficient and/or safemanner. Regardless of the type of device, it is often desirable for theimplantable medical device to communicate with another medical device.

SUMMARY

The present disclosure generally relates to systems, devices, andmethods for communicating information, and more particularly, tosystems, devices, and methods for communicating information betweenmedical devices in an energy adaptive manner. In some instances,communication signals used for communication between medical devices maycause an unwanted effect in the patient. For example, the communicationsignals may be communication pulses that are sufficiently energetic tocapture the heart, stimulate muscles and/or stimulate nerves. In someexample, when this occurs, a maximum energy level test (MELT) may beconducted where the amount of energy of the communication pulses may bechanged so as to identify an amount of energy that corresponds to anunwanted stimulation threshold. A maximum energy level for subsequentcommunication pulses may then be set below the unwanted stimulationthreshold, and subsequent communication between medical devices mayproceed. Reevaluating the unwanted stimulation threshold may occur fromtime to time and/or in response to a detected trigger event in order toprovide an energy adaptive communication protocol over time. The presentdisclosure also describes techniques for adjusting the energy level ofthe communication pulses to reduce the amount of energy used during suchcommunication while still achieving reliable communication.

In one example, a medical device comprises a communication moduleconfigured to deliver a plurality of pulses to tissue of a patient,where each pulse comprises an amount of energy; a control moduleoperatively coupled to the communication module, the control moduleconfigured to: for each delivered pulse, determine whether the deliveredpulse produces an unwanted stimulation of the patient; change the amountof energy of the plurality of pulses over time so as to identify anamount of energy that corresponds to an unwanted stimulation thresholdfor the communication pulses; set a maximum energy value forcommunication pulses that is below the unwanted stimulation threshold;and deliver communication pulses below the maximum energy value duringcommunication with another device.

Alternatively or additionally, in any of the above examples, to set themaximum energy value for communication pulses that is below the unwantedstimulation threshold, the controller may be configured to set themaximum energy value a predetermined safety margin below the unwantedstimulation threshold.

Alternatively or additionally, in any of the above examples, theunwanted stimulation may be a capture of a heart of the patient.

Alternatively or additionally, any of the above examples may furthercomprise a pulse generator module for delivering pacing pulses to tissueof the patient, wherein to deliver a plurality of pulses to tissue of apatient, the communication module is configured to deliver a pulse inlieu of the pulse generator module delivering a pacing pulse, and thepulse generator module is further configured to deliver a safety pacingpulse if the pulse did not capture the heart.

Alternatively or additionally, in any of the above examples, theunwanted stimulation may be a stimulation of a nerve of the patient.

Alternatively or additionally, in any of the above examples, theunwanted stimulation may be a stimulation of a muscle of the patient.

Alternatively or additionally, in any of the above examples, the amountof energy of each pulse is defined at least in part by an amplitude, apulse width, a morphology, or the specific vector via which the pulse isdelivered.

Alternatively or additionally, in any of the above examples, to changethe amount of energy of the plurality of pulses over time, thecontroller may be configured to change either the amplitude or the pulsewidth of each pulse.

Alternatively or additionally, in any of the above examples, to changethe amount of energy of the plurality of pulses over time, thecontroller may be configured to change both the amplitude and the pulsewidth of each pulse.

Alternatively or additionally, in any of the above examples, the medicaldevice may be further configured to deliver the plurality of pulses,change the amount of energy of the plurality of pulses, and set themaximum energy value for communication pulses that is below the unwantedstimulation threshold in a repeating manner.

Alternatively or additionally, in any of the above examples, the medicaldevice may be further configured to deliver the plurality of pulses,change the amount of energy of the plurality of pulses, and set themaximum energy value for communication pulses that is below the unwantedstimulation threshold in response to a trigger event.

Alternatively or additionally, in any of the above examples, the medicaldevice is a leadless cardiac pacemaker (LCP).

Alternatively or additionally, in any of the above examples, the anothermedical device is a subcutaneous implantable cardioverter-defibrillator(S-ICD).

Alternatively or additionally, in any of the above examples, the medicaldevice is an S-ICD.

Alternatively or additionally, in any of the above examples, the anothermedical device is an LCP.

In another example, a method for setting an energy level forcommunication pulses of a medical device comprises delivering aplurality of pulses to tissue of a patient, where each pulse includes anamount of energy, and for each delivered pulse, determining whether thedelivered pulse produces an unwanted stimulation of the patient;changing the amount of energy of the plurality of pulses over time so asto identify an amount of energy that corresponds to an unwantedstimulation threshold for the pulses; and setting a maximum energy valuefor communication pulses that is below the unwanted stimulationthreshold.

Alternatively or additionally, in any of the above examples, the maximumenergy value is set a predetermined safety margin below the unwantedstimulation threshold.

Alternatively or additionally, in any of the above examples, theunwanted stimulation is a capture of a heart of the patient.

Alternatively or additionally, in any of the above examples, deliveringa plurality of pulses to tissue of a patient comprises delivering apulse in lieu of a pacing pulse, and delivering a safety pacing pulse ifthe pulse did not capture the heart.

Alternatively or additionally, in any of the above examples, theunwanted stimulation is a stimulation of a nerve of the patient.

Alternatively or additionally, in any of the above examples, theunwanted stimulation is a stimulation of a muscle of the patient.

Alternatively or additionally, in any of the above examples, the amountof energy of each pulse is defined at least in part by an amplitude, apulse width, a morphology, or the specific vector via which the pulse isdelivered.

Alternatively or additionally, any of the above examples may furthercomprise repeating the delivering, changing and setting steps from timeto time.

Alternatively or additionally, any of the above examples may furthercomprise repeating the delivering, changing and setting steps inresponse to a trigger event.

In yet another example, a medical device comprises: a communicationmodule configured to deliver a plurality of pulses to tissue of apatient, where each pulse comprises an amount of energy; a controlmodule operatively coupled to the communication module, the controlmodule configured to: for each delivered pulse, determine whether thedelivered pulse produces an unwanted stimulation of the patient; changethe amount of energy of the plurality of pulses over time so as toidentify an amount of energy that corresponds to an unwanted stimulationthreshold for the pulses; set a maximum energy value for communicationpulses that is below the unwanted stimulation threshold; and delivercommunication pulses below the maximum energy value during communicationwith another device.

In still another example, a method for determining a minimumcommunication receive threshold for a medical device for use whenreceiving communication signals from another device comprises: settingthe minimum communication receive threshold to a first level;determining a number of detected communication signals with the minimumcommunication receive threshold at the first level; changing the minimumcommunication receive threshold to a second level, wherein the secondlevel is different than the first level; determining a number ofdetected communication signals with the minimum communication receivethreshold at the second level; determining a value for the minimumcommunication receive threshold based on the determined numbers ofdetected communication signals; setting the minimum communicationreceive threshold to the determined value; and using the set minimumcommunication receive threshold during subsequent communication betweenthe medical device and the another device.

Alternatively or additionally, in any of the above examples, at leastsome of the detected communication signals are noise signals interpretedby the medical device as communication signals when the minimumcommunication receive threshold is set at the second level.

Alternatively or additionally, in any of the above examples, determiningthe value for the minimum communication receive threshold based on thedetermined numbers of detected communication signals comprisesdetermining the value based on a signal to noise ratio.

Alternatively or additionally, any of the above examples may furthercomprise determining the number of detected communication signals withthe minimum communication receive threshold at the first level anddetermining the number of detected communication signals with theminimum communication receive threshold at the second level duringperiods of no intrinsic cardiac activity.

Alternatively or additionally, in any of the above examples, the secondlevel is less than the first level.

Alternatively or additionally, in any of the above examples, the secondlevel is greater than the first level.

In another example, a medical device comprises: a communication moduleconfigured to receive a plurality of communication signals from anotherdevice; a control module operatively coupled to the communicationmodule, the control module configured to: set a minimum communicationreceive threshold to a first level; determine a number of detectedcommunication signals with the minimum communication receive thresholdat the first level; change the minimum communication receive thresholdto a second level, wherein the second level is different than the firstlevel; determine a number of detected communication signals with theminimum communication receive threshold at the second level; determine avalue for the minimum communication receive threshold based on thedetermined number of detected communication signals; set the minimumcommunication receive threshold to the determined value; and use the setminimum communication receive threshold during subsequent communicationbetween the medical device and the other device.

Alternatively or additionally, in any of the above examples, the maximumenergy value is set a predetermined safety margin below the unwantedstimulation threshold.

In another example, a method for adjusting a communication protocolbetween a plurality of medical devices comprises: with a first medicaldevice, delivering one or more first pulses where each first pulseincludes a first amount of energy; determining a number of the one ormore first pulses received by a second medical device; with the firstmedical device, delivering one or more second pulses where each secondpulse includes a second amount of energy; determining a number of theone or more second pulses received by the second medical device; andadjusting a minimum communication pulse energy for the first medicaldevice when communicating with the second medical device based on thenumber of the one or more first pulses received by the second medicaldevice and the number of the one or more second pulses received by thesecond medical device.

Alternatively or additionally, in any of the above examples, the amountof energy of each pulse is defined at least in part by an amplitude, apulse width, a morphology, or the specific vector via which the pulse isdelivered.

Alternatively or additionally, in any of the above examples, adjustingthe minimum communication pulse energy for the first medical device whencommunicating with the second medical device comprises adjusting thepulse width of each communication pulse used to communicate with thesecond medical device.

Alternatively or additionally, in any of the above examples, adjustingthe minimum communication pulse energy for the first medical device whensubsequently communicating with the second medical device comprisesadjusting the amplitude of each communication pulse used to communicatewith the second medical device.

Alternatively or additionally, in any of the above examples, adjustingthe minimum communication pulse energy for the first medical device whensubsequently communicating with the second medical device comprisesadjusting the pulse width and the amplitude of each communication pulseused to communicate with the second medical device.

Alternatively or additionally, in any of the above examples, adjustingthe minimum communication pulse energy for the first medical device whencommunicating with the second medical device based on the number of theone or more first pulses received by the second medical device and thenumber of the one or more second pulses received by the second medicaldevice comprises setting the minimum communication pulse energy for thefirst medical device when communicating with the second medical deviceto the amount of energy of the one or more pulses with the lowestacceptable number of pulses received by the second medical device.

Alternatively or additionally, any of the above examples may furthercomprise adding a predetermined safety margin to the minimumcommunication pulse energy.

Alternatively or additionally, any of the above examples may furthercomprise determining whether the adjusted minimum communication pulseenergy overlaps a maximum energy threshold.

Alternatively or additionally, any of the above examples, may furthercomprise, after determining the adjusted minimum communication pulseenergy overlaps the maximum energy threshold, by the first medicaldevice, entering a safe communication mode.

The above summary is not intended to describe each embodiment or everyimplementation of the present disclosure. Advantages and attainments,together with a more complete understanding of the disclosure, willbecome apparent and appreciated by referring to the followingdescription and claims taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing description of various illustrative embodiments in connectionwith the accompanying drawings, in which:

FIG. 1 is a schematic block diagram of an illustrative leadless cardiacpacemaker (LCP) according to one example of the present disclosure;

FIG. 2 is a schematic block diagram of another illustrative medicaldevice that may be used in conjunction with the LCP of FIG. 1;

FIG. 3 is a schematic diagram of an exemplary medical system thatincludes multiple LCPs and/or other devices in communication with oneanother;

FIG. 4 is a schematic diagram of a system including an LCP and anothermedical device, in accordance with yet another example of the presentdisclosure;

FIG. 5 is a schematic diagram of a system including an LCP and anothermedical device, in accordance with another example of the presentdisclosure;

FIG. 6 is a graphical representation of an example sensed signalincluding communication pulses and noise signals, in accordance with anexample of the present disclosure;

FIG. 7 is a graphical representation of an example sensed signalincluding communication pulses and noise signals, in accordance with anexample of the present disclosure;

FIG. 8 is a graphical representation of an example sensed signalincluding communication pulses and noise signals, in accordance with anexample of the present disclosure;

FIG. 9 is a graphical representation of an example sensed signalincluding communication pulses and noise signals, in accordance with anexample of the present disclosure;

FIG. 10 is a graphical representation of an example sensed signalincluding communication pulses and noise signals, in accordance with anexample of the present disclosure;

FIG. 11 is a graphical representation of an example sensed signalincluding communication pulses and noise signals, in accordance with anexample of the present disclosure;

FIG. 12 is a graphical representation of an example communication pulse,in accordance with an example of the present disclosure;

FIG. 13 is a graphical representation of a strength-duration curve, inaccordance with an example of the present disclosure;

FIG. 14 is a flow diagram of an illustrative method that may beimplemented by a medical device or medical device system, such as theillustrative medical devices and medical device systems described withrespect to FIGS. 1-2 and 4-5;

FIG. 15 is a flow diagram of an illustrative method that may beimplemented by a medical device or medical device system, such as theillustrative medical devices and medical device systems described withrespect to FIGS. 1-2 and 4-5; and

FIG. 16 is a flow diagram of an illustrative method that may beimplemented by a medical device or medical device system, such as theillustrative medical devices and medical device systems described withrespect to FIGS. 1-2 and 4-5.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit aspects of thedisclosure to the particular illustrative embodiments described. On thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure.

DESCRIPTION

The following description should be read with reference to the drawingsin which similar elements in different drawings are numbered the same.The description and the drawings, which are not necessarily to scale,depict illustrative embodiments and are not intended to limit the scopeof the disclosure.

This disclosure describes systems, devices, and methods forcommunicating information, and more particularly, to systems, devices,and methods for communicating information between medical devices in anenergy adaptive manner. In some instances, communication signals usedfor communication between medical devices may cause an unwanted effectin the patient. For example, the communication signals may becommunication pulses that are sufficiently energetic to capture theheart, stimulate muscles and/or stimulate nerves. In some example, whenthis occurs, a maximum energy level test (MELT) may be conducted wherethe amount of energy of the communication pulses may be changed so as toidentify an amount of energy that corresponds to an unwanted stimulationthreshold. A maximum energy level for subsequent communication pulsesmay then be set below the unwanted stimulation threshold, and subsequentcommunication between medical devices may proceed. Reevaluating theunwanted stimulation threshold may occur from time to time and/or inresponse to a detected trigger event to provide energy adaptivecommunication over time. The present disclosure also describestechniques for adjusting the energy level of the communication pulses toreduce the amount of energy used during such communication while stillachieving reliable communication.

FIG. 1 is a conceptual drawing of an exemplary leadless cardiacpacemaker (LCP) that may be implanted into a patient and may operate tosense physiological signals and parameters and deliver one or more typesof electrical stimulation therapy to tissues of the patient. Exampleelectrical stimulation therapy includes anti-tachycardia pacing (ATP)therapy, cardiac resynchronization therapy (CRT), bradycardia therapy,various types of pacing therapy including rate responsive pacingtherapy, and/or the like. As can be seen in FIG. 1, LCP 100 may be acompact device with all components housed within LCP 100 or directly onhousing 120. LCP 100 may include communication module 102, pulsegenerator module 104, electrical sensing module 106, mechanical sensingmodule 108, processing module 110, energy storage module 112, andelectrodes 114.

As depicted in FIG. 1, LCP 100 may include electrodes 114, which can besecured relative to housing 120 but exposed to the tissue and/or bloodsurrounding LCP 100. Electrodes 114 may generally conduct electricalsignals to and from LCP 100 and the surrounding tissue and/or blood.Such electrical signals can include communication pulses, electricalstimulation pulses, and intrinsic cardiac electrical signals. Intrinsiccardiac electrical signals may consist of the electrical signalsgenerated by the heart and may be represented by an electrocardiogram(ECG). Electrodes 114 can be made up of one or more biocompatibleconductive materials such as various metals or alloys that are known tobe safe for implantation within a human body. In some instances,electrodes 114 may be generally disposed on either end of LCP 100 andmay be in electrical communication with one or more of modules 102, 104,106, 108, and 110. In examples where electrodes 114 are secured directlyto housing 120, electrodes 114 may have an insulative portion thatelectrically isolates electrodes 114 from adjacent electrodes, housing120, and/or other portions of LCP 100. Some or all of electrodes 114 maybe spaced from housing 120 and connected to housing 120 and/or othercomponents of LCP 100 through connecting wires. In such embodiments, theelectrodes 114 may be placed on a on a tail that extends from thehousing 120. As shown in FIG. 1, in some examples, LCP 100 mayadditionally include electrodes 114′. Electrodes 114′ are similar toelectrodes 114 except that electrodes 114′ are disposed on the sides ofLCP 100 and increase the number of electrodes by which LCP 100 maydeliver communication pulses and electrical stimulation pulses and/orsense for intrinsic cardiac electrical signals, communication pulses,and/or electrical stimulation pulses.

Electrodes 114 and/or 114′ may have any of a variety of sizes and/orshapes, and may be spaced at any of a variety of distances. For example,electrodes 114 may have a diameter of two to twenty millimeters (mm).However, in other examples, electrodes 114 and/or 114′ may have adiameter of two, three, five, seven millimeters (mm), or any othersuitable diameter, dimension and shape. Example lengths for electrodes114 and/or 114′ include a length of zero, one, three, five, tenmillimeters (mm), or any other suitable length. As used herein, thelength is a dimension of electrodes 114 and/or 114′ that extends awayfrom housing 120. Additionally, at least some of electrodes 114 and/or114′ may be spaced from one another by a distance of twenty, thirty,forty, fifty millimeters (mm), or any other suitable distance. Theelectrodes 114 and/or 114′ of a single device may have different sizeswith respect to each other, and the spacing of the electrodes on thedevice may not be uniform.

Communication module 102 may be electrically coupled to electrodes 114and/or 114′ and configured to deliver communication pulses to tissues ofthe patient for communicating with other devices such as sensors,programmers, other medical devices, and the like. Communication pulses,as used herein, may be any modulated signal that conveys information toanother device, either by itself or in conjunction with one or moreother modulated signals. In some examples, communication pulses arelimited to only including sub-threshold signals which conveyinformation. Such other devices may be located either external orinternal to the patient's body. Communication module 102 mayadditionally be configured to sense for communication pulses deliveredby the other devices, which are located externally to LCP 100.Irrespective of the location, LCP and the other devices may communicatewith each other via communication module 102 to accomplish one or moredesired functions. Some example functions include storing communicateddata, using communicated data for determining occurrences ofarrhythmias, coordinating delivery of electrical stimulation therapy,and/or other functions.

LCP 100 and the other devices may use the delivered communication pulsesto communicate raw information, processed information, messages, and/orother data. Raw information may include information such as sensedelectrical signals (e.g. a sensed ECG), signals gathered from coupledsensors, and the like. In some examples, the raw information may includesignals that have been filtered using one or more signal processingtechniques. Processed information may include any information that hasbeen determined by LCP 100. For example, processed information mayinclude a determined heart rate, timings of determined heartbeats,timings of other determined events, determinations of thresholdcrossings, expirations of monitored time periods, and determinedparameters such as activity parameters, blood-oxygen parameters, bloodpressure parameters, heart sound parameters, and the like. Messages mayinclude instructions directing another device to take action,notifications of imminent actions of the sending device, requests forreading from the receiving device or writing data to the receivingdevice.

In at least some examples, communication module 102 (or LCP 100) mayfurther include switching circuitry to selectively connect one or moreof electrodes 114 and/or 114′ to communication module 102 in order toselect via which electrodes 114 and/or 114′ communication module 102delivers the communication pulses. Additionally, communication module102 may be configured to use one or more methods for communicating withother devices. For example, communication module 102 may communicate viaconducted signals, radiofrequency (RF) signals, optical signals,acoustic signals, inductive coupling, and/or any other signals ormethods suitable for communication.

Pulse generator module 104 of LCP 100 may also be electrically connectedto one or more of electrodes 114 and/or 114′. Pulse generator module 104may be configured to generate electrical stimulation pulses and deliverthe electrical stimulation pulses to tissues of a patient via electrodes114 and/or 114′electrodes in order to effectuate one or more electricalstimulation therapies. Electrical stimulation pulses as used herein aremeant to encompass any electrical signals that may be delivered totissue of a patient for purposes of treatment of any type of disease orabnormality. When used to treat heart diseases or abnormalities, theelectrical stimulation pulses may generally be configured so as tocapture the heart of the patient—cause the heart to contract in responseto the delivered electrical stimulation pulse. In at least exampleswhere pulse generator 104 is configured to generate specific types ofelectrical stimulation pulses termed defibrillation/cardioversionpulses, pulse generator module 104 may include one or more capacitorelements.

Pulse generator module 104 may include capability to modify theelectrical stimulation pulses, such as by adjusting a pulse width oramplitude of the electrical stimulation pulses, in order to ensure thatthe delivered electrical stimulation pulses consistently capture theheart. Pulse generator module 104 may use energy stored in energystorage module 112 to generate the electrical stimulation pulses. In atleast some examples, pulse generator module 104 (or LCP 100) may furtherinclude switching circuitry to selectively connect one or more ofelectrodes 114 and/or 114′ to pulse generator module 104 in order toselect via which electrodes 114 and/or 114′ pulse generator 104 deliversthe electrical stimulation pulses.

In some examples, LCP 100 may include electrical sensing module 106 andmechanical sensing module 108. Electrical sensing module 106 may beconfigured to sense intrinsic cardiac electrical signals conducted fromelectrodes 114 and/or 114′ to electrical sensing module 106. Forexample, electrical sensing module 106 may be electrically connected toone or more electrodes 114 and/or 114′ and electrical sensing module 106may be configured to receive cardiac electrical signals conductedthrough electrodes 114 and/or 114′. In some examples, the cardiacelectrical signals may represent local information from the chamber inwhich LCP 100 is implanted. For instance, if LCP 100 is implanted withina ventricle of the heart, cardiac electrical signals sensed by LCP 100through electrodes 114 and/or 114′ may represent ventricular cardiacelectrical signals. Mechanical sensing module 108 may include, or beelectrically connected to, various sensors, such as accelerometers,blood pressure sensors, heart sound sensors, blood-oxygen sensors,and/or other sensors which measure one or more physiological parametersof the heart and/or patient. Mechanical sensing module 108 may gathersignals from the sensors indicative of the various physiologicalparameters. Both electrical sensing module 106 and mechanical sensingmodule 108 may be further connected to processing module 110 and mayprovide signals representative of the sensed cardiac electrical signalsand/or physiological signals to processing module 110. Althoughdescribed with respect to FIG. 1 as separate sensing modules, in someexamples, electrical sensing module 106 and mechanical sensing module108 may be combined into a single module.

Processing module 110 may be configured to control the operation of LCP100. For example, processing module 110 may be configured to receivecardiac electrical signals from electrical sensing module 106 and/orphysiological signals from mechanical sensing module 108. Based on thereceived signals, processing module 110 may determine occurrences andtypes of arrhythmias. Processing module 110 may further receiveinformation from communication module 102. In some examples, processingmodule 110 may additionally use such received information to determineoccurrences and types of arrhythmias. However, in other examples, LCP100 may use the received information instead of the signals receivedfrom electrical sensing module 106 and/or mechanical sensing module108—for instance if the received information is more accurate than thesignals received from electrical sensing module 106 and/or mechanicalsensing module 108 or if electrical sensing module 106 and/or mechanicalsensing module 108 have been disabled or omitted from LCP 100.

Based on any determined arrhythmias, processing module 110 may thencontrol pulse generator module 104 to generate electrical stimulationpulses in accordance with one or more electrical stimulation therapiesto treat the determined arrhythmias. For example, processing module 110may control pulse generator module 104 to generate pacing pulses withvarying parameters and in different sequences to effectuate one or moreelectrical stimulation therapies. In controlling pulse generator module104 to deliver bradycardia pacing therapy, processing module 110 maycontrol pulse generator module 104 to deliver pacing pulses designed tocapture the heart of the patient at a regular interval to prevent theheart of a patient from falling below a predetermined threshold. For ATPtherapy, processing module 110 may control pulse generator module 104 todeliver pacing pulses at a rate faster than an intrinsic heart rate of apatient in attempt to force the heart to beat in response to thedelivered pacing pulses rather than in response to intrinsic cardiacelectrical signals. Processing module 110 may then control pulsegenerator module 104 to reduce the rate of delivered pacing pulses downto a safe level. In CRT, processing module 110 may control pulsegenerator module 104 to deliver pacing pulses in coordination withanother device to cause the heart to contract more efficiently.Additionally, in cases where pulse generator module 104 is capable ofgenerating defibrillation and/or cardioversion pulses fordefibrillation/cardioversion therapy, processing module 110 may controlpulse generator module 104 to generate such defibrillation and/orcardioversion pulses. In other examples, processing module 110 maycontrol pulse generator module 104 to generate electrical stimulationpulses to provide electrical stimulation therapies different than thosedescribed herein to treat one or more detected cardiac arrhythmias.

Aside from controlling pulse generator module 104 to generate differenttypes of electrical stimulation pulses and in different sequences, insome examples, processing module 110 may also control pulse generatormodule 104 to generate the various electrical stimulation pulses withvarying pulse parameters. For example, each electrical stimulation pulsemay have a pulse width and a pulse amplitude. Processing module 110 maycontrol pulse generator module 104 to generate the various electricalstimulation pulses with specific pulse widths and pulse amplitudes. Forexample, processing module 110 may cause pulse generator module 104 toadjust the pulse width and/or the pulse amplitude of electricalstimulation pulses if the electrical stimulation pulses are noteffectively capturing the heart. Such control of the specific parametersof the various electrical stimulation pulses may ensure that LCP 100 isable to provide effective delivery of electrical stimulation therapy.

In some examples, processing module 110 may further controlcommunication module 102 to send information to other devices. Forexample, processing module 110 may control communication module 102 togenerate one or more communication pulses for communicating with otherdevices of a system of devices. For instance, processing module 110 maycontrol communication module 102 to generate communication pulses inparticular sequences, where the specific sequences convey different datato other devices. Communication module 102 may also conduct any receivedcommunication signals to processing module 110 for potential action byprocessing module 110.

In further examples, processing module 110 may additionally controlswitching circuitry by which communication module 102 and pulsegenerator module 104 deliver communication pulses and electricalstimulation pulses to tissue of the patient. As described above, bothcommunication module 102 and pulse generator module 104 may includecircuitry for connecting one or more electrodes 114 and/114′ tocommunication module 102 and pulse generator module 104 so those modulesmay deliver the communication pulses and electrical stimulation pulsesto tissue of the patient. The specific combination of one or moreelectrodes by which communication module 102 and pulse generator module104 deliver communication pulses and electrical stimulation pulsesinfluence the reception of communication pulses and/or the effectivenessof electrical stimulation pulses. Although it was described that each ofcommunication module 102 and pulse generator module 104 may includeswitching circuitry, in some examples LCP 100 may have a singleswitching module connected to all of communication module 102, pulsegenerator module 104, and electrodes 114 and/or 114′. In such examples,processing module 110 may control the single switching module to connectmodules 102/104 and electrodes 114/114′.

In some examples, processing module 110 may include a pre-programmedchip, such as a very-large-scale integration (VLSI) chip or anapplication specific integrated circuit (ASIC). In such embodiments, thechip may be pre-programmed with control logic in order to control theoperation of LCP 100. By using a pre-programmed chip, processing module110 may use less power than other programmable circuits while able tomaintain basic functionality, thereby increasing the battery life of LCP100. In other examples, processing module 110 may include a programmablemicroprocessor or the like. Such a programmable microprocessor may allowa user to adjust the control logic of LCP 100 after manufacture, therebyallowing for greater flexibility of LCP 100 than when using apre-programmed chip.

Processing module 110, in additional examples, may further include amemory circuit and processing module 110 may store information on andread information from the memory circuit. In other examples, LCP 100 mayinclude a separate memory circuit (not shown) that is in communicationwith processing module 110, such that processing module 110 may read andwrite information to and from the separate memory circuit. The memorycircuit, whether part of processing module 110 or separate fromprocessing module 110 may have address lengths of, for example, eightbits. However, in other examples, the memory circuit may have addresslengths of sixteen, thirty-two, or sixty-four bits, or any other bitlength that is suitable. Additionally, the memory circuit may bevolatile memory, non-volatile memory, or a combination of both volatilememory and non-volatile memory.

Energy storage module 112 may provide a power source to LCP 100 for itsoperations. In some examples, energy storage module 112 may be anon-rechargeable lithium-based battery. In other examples, thenon-rechargeable battery may be made from other suitable materials knownin the art. Because LCP 100 is an implantable device, access to LCP 100may be limited. In such circumstances, it is necessary to havesufficient energy capacity to deliver therapy over an extended period oftreatment such as days, weeks, months, or years. In some examples,energy storage module 112 may a rechargeable battery in order tofacilitate increasing the useable lifespan of LCP 100. In still otherexamples, energy storage module 112 may be other types of energy storagedevices such as capacitors.

To implant LCP 100 inside a patient's body, an operator (e.g., aphysician, clinician, etc.), may fix LCP 100 to the cardiac tissue ofthe patient's heart. To facilitate fixation, LCP 100 may include one ormore anchors 116. Anchor 116 may include any number of fixation oranchoring mechanisms. For example, anchor 116 may include one or morepins, staples, threads, screws, helix, tines, and/or the like. In someexamples, although not shown, anchor 116 may include threads on itsexternal surface that may run along at least a partial length of anchor116. The threads may provide friction between the cardiac tissue and theanchor to help fix anchor 116 within the cardiac tissue. In otherexamples, anchor 116 may include other structures such as barbs, spikes,or the like to facilitate engagement with the surrounding cardiactissue.

FIG. 2 depicts an example of another device, medical device (MD) 200,which may operate to sense physiological signals and parameters anddeliver one or more types of electrical stimulation therapy to tissuesof the patient. In the example shown, MD 200 may include a communicationmodule 202, a pulse generator module 204, an electrical sensing module206, a mechanical sensing module 208, a processing module 210, and anenergy storage module 218. Each of modules 202, 204, 206, 208, and 210may be similar to modules 102, 104, 106, 108, and 110 of LCP 100.Additionally, energy storage module 218 may be similar to energy storagemodule 112 of LCP 100. However, in some examples, MD 200 may have alarger volume within housing 220. In such examples, MD 200 may include alarger energy storage module 218 and/or a larger processing module 210capable of handling more complex operations than processing module 110of LCP 100.

While MD 200 may be another leadless device such as shown in FIG. 1, insome instances MD 200 may include leads, such as leads 212. Leads 212may include electrical wires that conduct electrical signals betweenelectrodes 214 and one or more modules located within housing 220. Insome cases, leads 212 may be connected to and extend away from housing220 of MD 200. In some examples, leads 212 are implanted on, within, oradjacent to a heart of a patient. Leads 212 may contain one or moreelectrodes 214 positioned at various locations on leads 212 and variousdistances from housing 220. Some leads 212 may only include a singleelectrode 214, while other leads 212 may include multiple electrodes214. Generally, electrodes 214 are positioned on leads 212 such thatwhen leads 212 are implanted within the patient, one or more of theelectrodes 214 are positioned to perform a desired function. In somecases, the one or more of the electrodes 214 may be in contact with thepatient's cardiac tissue. In other cases, the one or more of theelectrodes 214 may be positioned subcutaneously but adjacent thepatient's heart. The electrodes 214 may conduct intrinsically generatedelectrical cardiac signals to leads 212. Leads 212 may, in turn, conductthe received electrical cardiac signals to one or more of the modules202, 204, 206, and 208 of MD 200. In some cases, MD 200 may generateelectrical stimulation signals, and leads 212 may conduct the generatedelectrical stimulation signals to electrodes 214. Electrodes 214 maythen conduct the electrical stimulation signals to the cardiac tissue ofthe patient (either directly or indirectly). MD 200 may also include oneor more electrodes 214 not disposed on a lead 212. For example, one ormore electrodes 214 may be connected directly to housing 220.

Leads 212, in some examples, may additionally contain one or moresensors, such as accelerometers, blood pressure sensors, heart soundsensors, blood-oxygen sensors, and/or other sensors which are configuredto measure one or more physiological parameters of the heart and/orpatient. In such examples, mechanical sensing module 208 may be inelectrical communication with leads 212 and may receive signalsgenerated from such sensors.

While not required, in some examples MD 200 may be an implantablemedical device. In such examples, housing 220 of MD 200 may be implantedin, for example, a transthoracic region of the patient. Housing 220 maygenerally include any of a number of known materials that are safe forimplantation in a human body and may, when implanted, hermetically sealthe various components of MD 200 from fluids and tissues of thepatient's body. In such examples, leads 212 may be implanted at one ormore various locations within the patient, such as within the heart ofthe patient, adjacent to the heart of the patient, adjacent to the spineof the patient, or any other desired location.

In some examples, MD 200 may be an implantable cardiac pacemaker (ICP).In these examples, MD 200 may have one or more leads, for example leads212, which are implanted on or within the patient's heart. The one ormore leads 212 may include one or more electrodes 214 that are incontact with cardiac tissue and/or blood of the patient's heart. MD 200may be configured to sense intrinsically generated cardiac electricalsignals and determine, for example, one or more cardiac arrhythmiasbased on analysis of the sensed signals. MD 200 may be configured todeliver CRT, ATP therapy, bradycardia therapy, and/or other therapytypes via leads 212 implanted within the heart. In some examples, MD 200may additionally be configured to provide defibrillation/cardioversiontherapy.

In some instances, MD 200 may be an implantablecardioverter-defibrillator (ICD). In such examples, MD 200 may includeone or more leads implanted within a patient's heart. MD 200 may also beconfigured to sense electrical cardiac signals, determine occurrences oftachyarrhythmias based on the sensed electrical cardiac signals, anddeliver defibrillation and/or cardioversion therapy in response todetermining an occurrence of a tachyarrhythmia. In other examples, MD200 may be a subcutaneous implantable cardioverter-defibrillator(S-ICD). In examples where MD 200 is an S-ICD, one of leads 212 may be asubcutaneously implanted lead. In at least some examples where MD 200 isan S-ICD, MD 200 may include only a single lead which is implantedsubcutaneously but outside of the chest cavity, however this is notrequired.

In some examples, MD 200 may not be an implantable medical device.Rather, MD 200 may be a device external to the patient's body, andelectrodes 214 may be skin-electrodes that are placed on a patient'sbody. In such examples, MD 200 may be able to sense surface electricalsignals (e.g. electrical cardiac signals that are generated by the heartor electrical signals generated by a device implanted within a patient'sbody and conducted through the body to the skin) In such examples, MD200 may be configured to deliver various types of electrical stimulationtherapy, including, for example, defibrillation therapy.

FIG. 3 illustrates an example of a medical device system and acommunication pathway through which multiple medical devices 302, 304,306, and/or 310 of the medical device system may communicate. In theexample shown, medical device system 300 may include LCPs 302 and 304,external medical device 306, and other sensors/devices 310. Externaldevice 306 may be a device disposed external to a patient's body, asdescribed previously with respect to MD 200. Other sensors/devices 310may be any of the devices described previously with respect to MD 200,such as ICPs, ICDs, and S-ICDs. Other sensors/devices 310 may alsoinclude various diagnostic sensors that gather information about thepatient, such as accelerometers, blood pressure sensors, or the like. Insome cases, other sensors/devices 310 may include an external programmerdevice that may be used to program one or more devices of system 300.

Various devices of system 300 may communicate via communication pathway308. For example, LCPs 302 and/or 304 may sense intrinsic cardiacelectrical signals and may communicate such signals to one or more otherdevices 302/304, 306, and 310 of system 300 via communication pathway308. In one example, one or more of devices 302/304 may receive suchsignals and, based on the received signals, determine an occurrence ofan arrhythmia. In some cases, device or devices 302/304 may communicatesuch determinations to one or more other devices 306 and 310 of system300. In some cases, one or more of devices 302/304, 306, and 310 ofsystem 300 may take action based on the communicated determination of anarrhythmia, such as by delivering a suitable electrical stimulation tothe heart of the patient. One or more of devices 302/304, 306, and 310of system 300 may additionally communicate command or response messagesvia communication pathway. The command messages may cause a receivingdevice to take a particular action whereas response messages may includerequested information or a confirmation that a receiving device did, infact, receive a communicated message or data.

It is contemplated that the various devices of system 300 maycommunicate via pathway 308 using RF signals, inductive coupling,optical signals, acoustic signals, or any other signals suitable forcommunication. Additionally, in at least some examples, the variousdevices of system 300 may communicate via pathway 308 using multiplesignal types. For instance, other sensors/device 310 may communicatewith external device 306 using a first signal type (e.g. RFcommunication) but communicate with LCPs 302/304 using a second signaltype (e.g. conducted communication). Further, in some examples,communication between devices may be limited. For instance, as describedabove, in some examples, LCPs 302/304 may communicate with externaldevice 306 only through other sensors/devices 310, where LCPs 302/304send signals to other sensors/devices 310, and other sensors/devices 310relay the received signals to external device 306.

In some cases, the various devices of system 300 may communicate viapathway 308 using conducted communication signals. Accordingly, devicesof system 300 may have components that allow for such conductedcommunication. For instance, the devices of system 300 may be configuredto transmit conducted communication signals (e.g. current and/or voltagepulses) into the patient's body via one or more electrodes of atransmitting device, and may receive the conducted communication signals(e.g. pulses) via one or more electrodes of a receiving device. Thepatient's body may “conduct” the conducted communication signals (e.g.pulses) from the one or more electrodes of the transmitting device tothe electrodes of the receiving device in the system 300. In suchexamples, the delivered conducted communication signals (e.g. pulses)may differ from pacing pulses, defibrillation and/or cardioversionpulses, or other electrical stimulation therapy signals. For example,the devices of system 300 may deliver electrical communication pulses atan amplitude/pulse width that is sub-threshold. That is, thecommunication pulses have an amplitude/pulse width designed to notcapture the heart. Although, in some cases, the amplitude/pulse width ofthe delivered electrical communication pulses may be above the capturethreshold of the heart, but may be delivered during a refractory periodof the heart and/or may be incorporated in or modulated onto a pacingpulse, if desired.

Delivered electrical communication pulses may be modulated in anysuitable manner to encode communicated information. In some cases, thecommunication pulses may be pulse width modulated and/or amplitudemodulated. Alternatively, or in addition, the time between pulses may bemodulated to encode desired information. In some cases, conductedcommunication pulses may be voltage pulses, current pulses, biphasicvoltage pulses, biphasic current pulses, or any other suitableelectrical pulse as desired.

FIGS. 4 and 5 show illustrative medical device systems that may beconfigured to operate according to techniques disclosed herein. Forexample, the systems may include multiple devices that are implantedwithin a patient and are configured to sense physiological signals,determine occurrences of cardiac arrhythmias, and deliver electricalstimulation to treat detected cardiac arrhythmias. In FIG. 4, an LCP 402is shown fixed to the interior of the left ventricle of the heart 410,and a pulse generator 406 is shown coupled to a lead 412 having one ormore electrodes 408 a-408 c. In some cases, the pulse generator 406 maybe part of a subcutaneous implantable cardioverter-defibrillator(S-ICD), and the one or more electrodes 408 a-408 c may be positionedsubcutaneously adjacent the heart. LCP 402 may communicate with theS-ICD, such as via communication pathway 308. The locations of LCP 402,pulse generator 406, lead 412, and electrodes 408 a-c depicted in FIG. 4are just exemplary. In other examples of system 400, LCP 402 may bepositioned in the right ventricle, right atrium, or left atrium of theheart, as desired. In still other examples, LCP 402 may be implantedexternally adjacent to heart 410 or even remote from heart 410.

In FIG. 5, an LCP 502 is shown fixed to the interior of the leftventricle of the heart 510, and a pulse generator 506 is shown coupledto a lead 512 having one or more electrodes 504 a-504 c. In some cases,the pulse generator 506 may be part of an implantable cardiac pacemaker(ICP) and/or an implantable cardioverter-defibrillator (ICD), and theone or more electrodes 504 a-504 c may be positioned in the heart 510.In some cases, LCP 502 may communicate with the implantable cardiacpacemaker (ICP) and/or an implantable cardioverter-defibrillator (ICD),such as via communication pathway 308. As with FIG. 4, the locations ofLCP 502, pulse generator 506, lead 512, and electrodes 504 a-c depictedin FIG. 5 are just exemplary. In other examples of system 500, LCP 502may be positioned in the right ventricle, right atrium, or left atriumof the heart, as desired. In still other examples, LCP 502 may beimplanted externally adjacent to heart 510 or even remote from heart510. Additionally, in some examples lead 512 and/or electrodes 504 a-cmay be disposed in different chambers of heart 510, or pulse generatormay include additional leads and/or electrodes that are disposed withinor adjacent to heart 510.

The medical device systems 400 and 500 may also include an externalsupport device, such as external support devices 420 and 520. Externalsupport devices 420 and 520 can be used to perform functions such asdevice identification, device programming and/or transfer of real-timeand/or stored data between devices using one or more of thecommunication techniques described herein. As one example, communicationbetween external support device 420 and the pulse generator 406 isperformed via a wireless mode, and communication between the pulsegenerator 406 and LCP 402 is performed via a conducted mode. In someexamples, communication between the LCP 402 and external support device420 is accomplished by sending communication information through thepulse generator 406. However, in other examples, communication betweenthe LCP 402 and external support device 420 may be via a communicationmodule.

FIGS. 4-5 only illustrate a few examples of medical device systems thatmay be configured to operate according to techniques disclosed herein.Other example medical device systems may include additional or differentmedical devices and/or configurations. For instance, other medicaldevice systems that are suitable to operate according to techniquesdisclosed herein may include additional LCPs implanted within the heart.Another example medical device system may include a plurality of LCPswith or without other devices such as pulse generator 406 or 506, withat least one LCP capable of delivering defibrillation therapy. Stillanother example may include one or more LCPs implanted along with atransvenous pacemaker and with or without an implanted SICD. In yetother examples, the configuration or placement of the medical devices,leads, and/or electrodes may be different from those depicted in FIGS. 4and 5. Accordingly, it should be recognized that numerous other medicaldevice systems, different from those depicted in FIGS. 4 and 5, may beoperated in accordance with techniques disclosed herein. As such, theexamples systems shown in FIGS. 4 and 5 should not be viewed as limitingin any way.

Even further, the disclosed techniques may be applied to devices thatare not configured to detect and treat cardiac arrhythmias. For example,the techniques disclosed herein may be applicable to any medical devicesor sensors which communicate with other devices and/or sensors.Accordingly, although the below examples are described with respect toan LCP device and an S-ICD device, this disclosure should not beconstrued to be so limiting. Additionally, the term ‘communicationpulses’ as used below may correspond to pulses of any of thecommunication modalities mentioned previously, such as RF pulses,acoustic pulses, optical pulses, inductive pulses, and/or conductedpulses.

Using the system of FIG. 4 as one exemplary embodiment, LCP 402 and anS-ICD device (which can include pulse generator 406) may communicatewith each other to, for example, detect cardiac abnormalities and totreat the detected cardiac abnormalities. As discussed above, LCP 402and the S-ICD may communicate by sending communication pulses back andforth. The communication modules of both devices may be constantlylistening for communication pulses and conveying any receivedcommunication pulses to processing units for further action. Because thecommunication modules are constantly listening, the communicationmodules may also receive signals other than communication pulses, forexample noise signals. While in this example bi-directionalcommunication is used, it is contemplated that in some systems onlyuni-directional communication may be used.

One issue that a device may encounter is interpreting noise signals ascommunication pulses. To combat interpreting noise signals ascommunication pulses, a device may employ a minimum communicationreceive threshold (MCRT). A MCRT may be a minimum energy threshold, anda device may only interpret received signals with energy levels abovethe MCRT as communication pulses. Of course, a device may employ othermechanisms for determining whether received signals are communicationpulses (rather than noise signals or other signals), such as byanalyzing the morphology or other features of the received signals.Another example mechanism for distinguishing between communicationpulses and noise or other signals may be to use a pulse positionparameter. For example, the device delivering the communication pulsesmay be configured to deliver the pulses at predetermined times orintervals of time. In such examples, if the receiving device received asignal that might appear to be a communication pulse but occurredoutside of the predetermined times or intervals of time, the receivingdevice would interpret the received signal as other than a communicationpulse. Such other mechanisms may be employed in place of an MCRT or inaddition to an MCRT.

When a device determines that a received signals is a communicationpulse, for example because the received signal has an energy level abovethe device's MCRT, and in some examples the received signal passes oneor more other tests for whether the received signal is a communicationpulse, the device may forward the received signal to one or more modulesof the device for additional processing.

If the MCRT is set too low, noise may exceed the MCRT and may beimproperly interpreted as a communication pulse. This can reduce thereliability and accuracy of the communicated data. When the MCRT is settoo high, namely above what is required to reliably receivecommunication pulses, the sending medical device may expend extra energysending each communication pulse. Since many medical devices have alimited power supply (e.g. a battery or other energy storage module),reducing the energy expended by each communication pulse can be animportant consideration, and in some cases may substantially increasethe useful life of the medical device.

Accordingly, to ensure that the MCRT is set to an appropriate level, adevice, for example, LCP 402 and/or the S-ICD, may periodically performan MCRT test. Typical periods between performing an MCRT test includeonce a day, once a week, once a month, or any other suitable period oftime. In other examples, a device may perform an MCRT test based ontrigger events, for example upon detection of a threshold amount ofignored communication attempts, temperature changes, voltage changes, ordelivery of one or more therapies. For instance, a first device may sendcommunication pulses to a second device that would normally cause thesecond device to response with one or more communication pulses. Thefirst device may count a number of times that the first device hasissued a communication without receiving a response from the seconddevice. After the count reaches a threshold amount, the first device maytrigger the second device to perform an MCRT test. In such examples, thefirst device may communicate the trigger to the second device using analternative communication method, or the first device may adjust one ormore parameters of the communication pulses before communicating thetrigger to the second device, such as increasing the energy level of thecommunication pulses to a high level. In addition to the foregoing, andin some cases, a trigger event may include other events such as a changein a device parameter (e.g. pacing rate), a change in a patientsactivity (change in hemodynamic demand), a change in a patients posture,a detected patient event (e.g. defibrillation shock), a change in acommunication parameter (e.g. frequency). A device may perform an MCRTtest at implant, periodically and/or upon trigger events.

FIGS. 6-8 depict an example of received signals by a device, such as LCP402, during MCRT tests. In some examples, LCP 402 may use the voltage ofthe received signals as a measure of an energy level of the receivedsignals. In such examples, LCP 402 may set a voltage threshold as theMCRT, represented by voltage threshold 604. However, in other examples,LCP 402 may use other measures of energy to set a threshold as the MCRTduring MCRT tests, for the example electrical power of the signal or theelectrical energy of the signal. FIG. 6 depicts signal 600, which is anexample signal received by LCP 402 during an MCRT test. During the MCRTtest, LCP 402 may coordinate with the S-ICD for the S-ICD to deliverpulses to tissue of a patient during a predetermined period of time. Insome examples, the pulses may be communication pulses. In otherexamples, the pulses may be test pulses. The test pulses may havesimilar parameters as communication pulses (e.g. pulse widths andamplitudes). However, the test pulses may not be configured to conveyinformation to the receiving device, or the S-ICD may not deliver thetest pulses in combinations which would convey information. The pulsesmay be different than stimulation and/or defibrillation pulses that theS-ICD may be configured to deliver during delivery of electricalstimulation therapy. Signal 600 may be received by LCP 402 during thatpredetermined period of time. The predetermined period of time may be aportion of the cardiac cycle between heartbeats—e.g. after a T-wave butbefore a subsequent P-wave. In other examples, the predetermined periodof time may span multiple cardiac cycles. For instance, thepredetermined period of time may include multiple non-consecutiveperiods of time, wherein each period of time is the portion of thecardiac cycle between heartbeats.

In any case, the S-ICD may be configured to deliver one or more pulses,such as pulses 602 a-b, during the predetermined time period. The S-ICDmay be configured in many different ways to deliver the pulses. Forexample, the S-ICD may be configured to deliver a set amount of pulsesat regular intervals or at random intervals during the predeterminedtime period. Alternatively, the S-ICD may be configured to deliver arandom or bounded-random number of pulses either at regular or irregularintervals during the predetermined time period. In some cases, theprotocol by which the S-ICD delivers pulses during the MCRT test is alsoknown to LCP 402. Accordingly, LCP 402 may know the timing and/or numberof pulses that the S-ICD delivers during the MCRT test. Alternatively,the S-ICD may send a separate communication after the MCRT test to LCP402 indicating the number of pulses the S-ICD delivered during the MCRTtest.

During the MCRT test, LCP 402 may be receiving signals including pulsesdelivered by the S-ICD and various noise signals or other signals. Insignal 600, pulses are represented by pulses 602 a-b and noise or othersignals are represented by the jagged portions before, between, andafter pulses 602 a-b. As depicted by markers 608, LCP 402 may count thenumber of times signal 600 crosses from below voltage threshold 604 toabove voltage threshold 604. Once the predetermined time period hasended, LCP 402 may compare the number of detected crossings of voltagethreshold 604 with the number of pulses delivered by the S-ICD. If thetwo numbers are acceptable, LCP 402 may then use voltage threshold 604as the MCRT for future communications. In some examples, the numbers maybe acceptable if the numbers match—e.g. the number of crossings ofvoltage threshold 604 equal the number of delivered pulses. However, inother examples, the numbers may be acceptable if the number of deliveredpulses and the number of detected crossings of voltage threshold 604 arewithin a certain percentage of each other, such as five percent, tenpercent, fifteen percent, twenty percent, or any other suitable percentor amount.

If the number of delivered pulses is lower than the number of detectedcrossings of voltage threshold 604, LCP 402 may set a new, highervoltage threshold and run the MCRT test again. LCP 402 may raise thevoltage threshold for the next MCRT test by two millivolts, fivemillivolts, seven millivolts, ten millivolts, fifteen millivolts, twentymillivolts, or any other suitable value. In other examples, LCP 402 mayraise the voltage threshold by a predetermined percentage of the currentvoltage threshold, such as three percent, five percent, seven percent,ten percent, fifteen percent, twenty percent, or any other suitablevalue. FIGS. 7 and 8 both depict MCRT tests including pulses 702 a-b and802 a-b, and with LCP 402 using successively higher voltage thresholds704 and 804, respectively. As can be seen, the detected crossings of thevoltage thresholds, as represented by markers 708 and 808, become fewerwith each successive increase of the voltage threshold. In the exampleof FIG. 8, the number of delivered pulses equals the number of detectedcrossings from below voltage threshold 804 to above voltage threshold804. Accordingly, LCP 402 may set the MCRT equal to voltage threshold804. In some cases, the MCRT may be set above the voltage threshold 804by a margin amount.

If the number of delivered pulses is higher than the number of detectedcrossings of a voltage threshold during an MCRT test, LCP 402 may thenset a new, lower voltage threshold and perform another MCRT test. Insuch situations, LCP 402 may have set the voltage threshold too highsuch that one or more of the delivered pulses did not reach the MCRTvoltage threshold. In some cases, the sending device (e.g. SICD in thisexample), may provide pulses that are high during the MCRT test to helpalleviate the number of times that the number of delivered pulses ishigher than the number of detected crossings of the voltage thresholdduring an MCRT.

In some examples, LCP 402 may employ an MCRT test where, even after LCP402 determines that the number of delivered pulses and the number ofdetected crossings of a voltage threshold during an MCRT test areacceptable, LCP 402 may still perform subsequent MCRT tests. Forinstance, in such examples, it may be possible for LCP 402 to set alower MCRT and still ignore a large portion of noise signals or othersignals. Reducing the MCRT in such a manner may thereby reduce theamount of energy used during communication. Accordingly, afterdetermining that the number of delivered pulses and the number ofdetected crossings of a voltage threshold during an MCRT test areacceptable, LCP 402 may perform other MCRT test with a new, lowervoltage threshold. Additional MCRT tests with stepped down voltagethresholds may be repeated until the number of delivered pulses and thenumber of detected crossings of a voltage threshold during an MCRT testare no longer comparatively acceptable.

In such examples, LCP 402 may lower the voltage threshold during asubsequent MCRT by a smaller amount than a last increase of the voltagethreshold. For instance, LCP 402 may lower the voltage threshold byone-quarter, one-third, one-half, two-thirds, three-quarters, or anyother suitable fraction of the last voltage threshold increase. UsingFIGS. 7 and 8 as an example, if the voltage increase between voltagethreshold 704 and voltage threshold 804 was ten millivolts, LCP 402 mayset a new voltage threshold that is two and a half millivolts lessvoltage threshold 804 (e.g. one-quarter of the increase of the voltagethreshold between voltage threshold 704 and voltage threshold 804)during a subsequent MCRT test. LCP 402 may perform multiple additionalMCRT tests with new voltage thresholds lower than voltage threshold 804by varying fractions of ten millivolts (e.g. five millivolts, six andtwo thirds millivolts, seven and a half millivolts, etc.) until thenumber of delivered pulses and detected crossings of the voltagethreshold during the MCRT test become unacceptable (e.g. the numbers nolonger match or fall within a predetermined percentage of each other).At this point, LCP 402 may then set the MCRT equal to the last voltagethreshold for which the numbers were acceptable (sometimes plus a marginamount). In the example of FIGS. 7 and 8, if the number of deliveredpulses and detected crossings of the voltage threshold were acceptablefor the MCRT test using a voltage threshold two and a half millivoltsless than voltage threshold 804 but were unacceptable for an MCRT testusing a voltage threshold five millivolts less than voltage threshold804, LCP 402 may set the MCRT equal to the voltage threshold that is twoand a half millivolts less than voltage threshold 804.

The above description is just one example of how an MCRT test mayoperate. In other examples, instead of beginning with a relatively lowvoltage threshold 604, LCP 402 may begin with a relatively high voltagethreshold and, for subsequent MCRT tests, may reduce the voltagethreshold. In such examples, LCP 402 may identify the lowest testedvoltage threshold for which the number of delivered pulses and detectedcrossings of the voltage threshold were acceptable and set the MCRT forfuture communications equal to that threshold (sometimes plus a margin).In still other examples, LCP 402 may perform one MCRT test, but evaluatethe results using differing thresholds. This example is depicted by FIG.9. As can be seen in FIG. 9, the single MCRT test results in a singlesignal 900, including pulses 902 a-b. LCP 402 may analyze signal 900using multiple voltage thresholds 904 a-c. For each voltage threshold,LCP 402 may count the number of crossings from below the voltagethresholds to above the voltage thresholds, as indicated by markers 908a-c.

In some examples, an MCRT test may include a timing aspect in additionto a threshold aspect. In MCRT tests which employ only a thresholdaspect, there could be situations where a voltage level of a deliveredpulse falls below the voltage threshold, but the voltage level of anoise or other signal rises above the voltage threshold. In suchsituations, the receiving device may erroneously end up counting anumber of received pulses equal to the number of delivered pulses. Inorder to combat against this type of error, the delivering device may beconfigured to deliver pulses at predetermined times or at apredetermined frequency. In such examples, the receiving device may onlycount the number of crossings of the voltage threshold if they occurredat the predetermined times or at the end of predetermined intervals(determined by the predetermined frequency). In additional examples, thereceiving device may employ a window around the predetermined times orend of predetermined intervals. The receiving device may the thresholdcrossings only if they occur within the windows.

FIGS. 10 and 11 illustrate an additional feature of at least some MCRTtests. FIG. 10 depicts signal 1000, including pulses 1002 a-b. As can beseen in FIG. 10, LCP 402 would be unable to set voltage threshold 1004at a value such that only pulses 1002 a-b would rise above voltagethreshold 1004. In these examples, LCP 402 may be unable to determine avoltage threshold where the number of detected crossings of the voltagethreshold is acceptable. LCP 402 may then send a communication to theS-ICD requesting that the S-ICD increase the energy level of thedelivered pulses. In this particular example, this means that the S-ICDwould increase the voltage amplitude of the delivered pulses. In otherexamples, the S-ICD may increase the pulse width, the electrical powerof the pulses, the electrical energy of the pulses, or some otherparameter. FIG. 11 depicts signal 1100, including communication pulses1102 a-b. In the example of FIG. 11, the S-ICD has increased the energylevel of the delivered communication pulses 1102 a-b (e.g. increased thevoltage amplitude). Now, pulses 1102 a-b do cross from below voltagethreshold 1104 to above voltage threshold 1104, as represented bymarkers 1108. LCP 402 may then proceed to determine a MCRT. Additionallyin such examples, aside from LCP 402 setting a MCRT for futurecommunications, the S-ICD may also change the energy level of deliveredcommunication pulses for future communications. The MCRT may be setabove the noise level by an amount that produces a desiredsignal-to-noise (SN) ratio.

In some cases, an MCRT test may be repeated multiple times with the samevoltage threshold to help confirm the results. If the number of signalcrossings from below the voltage thresholds to above the voltagethresholds changes with each repeated MCRT test, then a maximum countvalue, an average count value, a mean count value or any other suitablevalue may be used to determine if the number of delivered pulsesacceptably matches the detected crossings of the voltage threshold. Insome cases, a standard deviation of the number of signal crossings maybe calculated across multiple MCRT tests using the same voltagethreshold, and if the standard deviation is above a threshold deviation,the MCRT test may be deemed to have failed and the voltage threshold maybe increased. This is just one example.

Although the above MCRT test descriptions are illustrated with respectto LCP 402, each device of a medical device system may have its ownMCRT. Accordingly, each device of a system may independently determinean MCRT. In some cases, LCP 402 may determine a different MCRT for eachmedical device that provides pulses to the LCP 402. For example, LCP 402may determine a first MCRT for pulses provided by an S-ICD, a secondMCRT for pulses provided by another LCP, and a third MCRT for pulsesprovided by a diagnostic only sensor device. This is just an example.

Devices of a medical system may adjust other aspects of communication inorder to achieve energy usage reduction. For example, a device, such asLCP 402 and/or the S-ICD, may adjust the energy level of communicationpulses used during communication. As part of an MCRT test, or separatefrom an MCRT test, a device may periodically perform a communicationpulse Energy Level Reduction test (ELRT). Typical periods betweenperforming such ELRT tests may include once a day, once a week, once amonth, or any other suitable period of time. In other examples, a devicemay perform such a ELRT test based on trigger events, for example upondetection of a threshold amount of ignored communication attempts,temperature changes, voltage changes, or delivery of one or moretherapies. For instance, a first device may send communication pulses toa second device which would normally cause the second device to responsewith one or more communication pulses. The first device may count anumber of times that the first device has issued a communication withoutreceiving a response from the second device. After the count reaches athreshold amount, the first device may trigger the second device toperform a communication pulse ELRT test. In such examples, the firstdevice may communicate the trigger to the second device using analternative communication method, or the first device may adjust one ormore parameters of the communication pulses (e.g. raise the voltageamplitude to a high level) before communicating the trigger to thesecond device. In addition to the foregoing, and in some cases, atrigger event may include other events such as a change in a deviceparameter (e.g. pacing rate), a change in a patients activity (change inhemodynamic demand), a change in a patients posture, a detected patientevent (e.g. defibrillation shock), a change in a communication parameter(e.g. frequency). A device may perform a communication pulse ELRT test,at implant, periodically and/or upon trigger events.

FIG. 12 is an illustration of an example communication pulse, includingvarious features of the communication pulse. In the example of FIG. 12,communication pulse 1202 is a biphasic communication pulse with positivepolarity voltage amplitude 1204, negative polarity voltage amplitude1206, positive pulse width 1208, negative pulse width 1210, and totalpulse width 1212. Communication pulse 1002 should be construed only asone example of a communication pulse that a device may employ. Otherexample communication pulses may be monophasic, either positive polarityor negative polarity, and have any suitable morphology. Additionally, inat least some examples, there may be a time period between positivepulse width 1208 and negative pulse width 1210, if desired.

Communication pulse 1202 may have a total energy level, and the totalenergy level of communication pulse 1202 may be related to parameters ofcommunication pulse 1202 such as the amplitudes, pulse widths, andmorphology (or shape) of communication pulse 1202. For simplicity, thedescribed examples may focus on changing the energy of communicationpulse 1202 by changing the amplitude and/or pulse width or communicationpulse 1202, but in other examples, the energy level of communicationpulse 1202 may be changed by changing the morphology of communicationpulse 1202, or even the specific vector by which the delivering devicedelivers communication pulse 1202.

When a device, such as LCP 402 or the S-ICD, delivers a communicationpulse, the communication pulse will have a first energy level at thetime of delivery. When conducted communication is used, as thecommunication pulse travels through tissue of the patient, thecommunication pulse will attenuate and arrive at a receiving device witha second lower energy level. Accordingly, a delivering device needs toensure that the energy level of the communication pulse at the time ofdelivery is great enough such that when the communication pulse arrivesat the receiving device, the communication pulse still has sufficientenergy for the receiving device to recognize the communication pulse asa communication pulse and distinguish it from noise. In the examples ofFIGS. 6-9, this would mean the communication pulses would need to have avoltage level above the MCRT of the receiving device. However, if thedelivering device delivers communication pulses with a higher energylevel than the MCRT of the receiving device, the delivering device maybe using more stored energy than is required—as generating thecommunication pulses consumes energy that is typically stored in alimited energy source such as a battery or other energy storage module.Accordingly, by performing a communication pulse ELRT test, a device mayreduce the amount of energy used during communications by lowering theamount of energy used for to generate the communication pulses.

A device, for example LCP 402, may begin a communication pulse ELRT testby delivering pulses with relatively high energy levels. The deliveredpulses may be communication pulses, such as depicted with respect toFIG. 12, or test pulses which have similar features to communicationpulse 1202 but may not convey information to the receiving device. Inthe example of FIG. 12, this may mean that LCP 402 may deliver a firstsequence of one or more pulses 1202 during a predetermined time period,where the pulses have relatively high positive polarity voltageamplitude 1204 and/or negative polarity voltage amplitude 1206. Thereceiving device, for example the S-ICD, may count a number of signalsthat the S-ICD determined as communication pulses during thepredetermined time period (for example, by noting the number of signalswhich crossed an energy or other threshold). The predetermined period oftime may be a portion of the cardiac cycle between heartbeats—e.g. aftera T-wave but before a subsequent P-wave. In other examples, thepredetermined period of time may span multiple cardiac cycles. Forinstance, the predetermined period of time may include multiplenon-consecutive periods of time, wherein each period of time is theportion of the cardiac cycle between heartbeats.

In the communication pulse ELRT test, LCP 402, similar to the S-ICD asdescribed above with respect to MCRT tests, may be configured to delivera set amount of pulses at regular intervals or at random intervalsduring the predetermined time period. Alternatively, LCP 402 may beconfigured to deliver a random or bounded-random number of pulses eitherat regular or irregular intervals during the predetermined time period.In some cases, the protocol by which LCP 402 delivers pulses during thecommunication pulse energy level reduction test is also known to theS-ICD. Accordingly, the S-ICD may know the timing and/or number ofpulses that LCP 402 delivers during the communication pulse ELRT test.Alternatively, LCP 402 may send a separate communication after thecommunication pulse ELRT test to the S-ICD indicating the number ofpulses LCP 402 delivered during the communication pulse ELRT test.

If the number of delivered pulses and the number of pulses identified bythe S-ICD are acceptable, LCP 402 and the S-ICD may repeat thecommunication pulse ELRT test, with LCP 402 delivering pulses with lowerenergy levels. As described, the energy level of the pulses may berelated to a positive polarity voltage amplitude, for instance positivepolarity voltage amplitude 1204 of communication pulse 1202, a negativepolarity voltage amplitude, for instance negative polarity voltageamplitude 1206 of communication pulse 1202, and a pulse width, such aspulse widths 1208 and 1210 (or total pulse width 1212) of communicationpulse 1202. Accordingly, in order to produce pulses with lower energylevels, LCP 402 may reduce the positive polarity voltage amplitude ofthe delivered pulses, the negative polarity voltage amplitude of thedelivered pulses, the pulse widths of the pulses, or any combination ofthese parameters. LCP 402 and the S-ICD may repeat this process untilthe number of delivered pulses and the number of pulses identified bythe S-ICD are unacceptable. Once the numbers become unacceptable, LCP402 may set the energy level of communication pulses for use in futurecommunication equal to the lowest energy level for which the numberswere acceptable (sometimes plus a margin). For example, LCP 402 maygenerate communication pulses during future communications withparameters equal to the parameters of delivered pulses that had thelowest energy level for which the numbers were acceptable (sometimesplus a margin). If, during the initial sequence of the test, the numberswere unacceptable, then instead of repeating the process after loweringthe energy level of the delivered pulses, LCP 402 may instead raise theenergy level of the delivered pulses. In such circumstances, it may bethe case that the initial energy level of the delivered pulses was nothigh enough to meet the MCRT of the S-ICD.

Of course, the above description of the communication pulse ELRT test isonly one way in which LCP 402 and the S-ICD may perform a communicationpulse ELRT test. In other examples, LCP 402 may begin a communicationpulse energy level reduction test by delivering pulses with relativelylow energy levels. If the number of delivered pulses and the number ofpulses identified by the S-ICD are initially unacceptable, then LCP 402may increase the energy level of the pulses and repeat a deliverysequence.

As noted above, a communication pulse ELRT tests may include adding asafety margin to the energy levels of communication pulses used forfuture communications. For example, the attenuation of deliveredcommunication pulses may change as a function of the respiratory cycleof a patient or other biological processes. Accordingly, it is possiblethat even after LCP 402 determines an energy level of communicationpulses for use in future communications, delivering communication pulseswith that energy level may not reach the energy level of the S-ICD'sMCRT. In order to account for this variability, LCP 402 may add a safetymargin to the energy level of communication pulses determined based onthe communication pulse ELRT test. For example, LCP 402 may usecommunication pulses for future communications with energy levels fivepercent, ten percent, fifteen percent, twenty percent, or any othersuitable percentage level higher than the energy level determined by thecommunication pulse ELRT test.

The above example was described from the perspective of setting anenergy level for communication pulses for use in communications by LCP402. In some examples, each device of a medical device system mayperform a similar test to set an energy level for communication pulsesfor future communications. However, each communication pulse ELRT testmay determine an appropriate energy level for communication pulses foruse in communication between a pair of devices. For example, the amountof energy a communication pulse has when it arrives at a device may be afunction of the distance between the delivering device and the receivingdevice, the type of tissue between the devices, the respiratory cycle ofthe patient, and other biological or other factors. Accordingly, acommunication pulse delivered by a single device may arrive at multipledifferent devices with differing energy levels. Each device, then, mayperform a MCRT and/or communication pulse ELRT test with respect to eachother device of the system. Each test may determine an energy level ofcommunication pulses for use in communications between each deliveringdevice/receiving device pair. In some examples, each device may storethe results of each test, e.g. an association between a specific deviceand an energy level of communication pulses. Then, when a devicecommunicates information to another device, the delivering device maydeliver communication pulses with the energy level associated with thereceiving device that it has stored in memory. If a device communicatessimultaneously with multiple devices, the delivering device may usecommunication pulses with an energy level that is the highest of theenergy levels associated with the receiving devices. In other examples,a device may only store the highest energy level of communication pulsesafter performing a communication pulse energy level reduction test foreach other device in the system. This may reduce an amount of memoryrequired for storing energy level associations while ensuring that adelivering device can communicate with each other device of the system.

Some medical device systems may employ both MCRT tests and communicationpulse ELRT tests. In these systems, the devices may first perform anMCRT test to determine an appropriate minimum communication receivethreshold (MCRT). Setting the MCRT to an appropriate level firstestablishes a floor for communication pulse energy levels. In somecases, these MCRT tests may be performed at implant, at scheduled times,in response to detected trigger events, and/or at any other suitabletimes. After the MCRT tests, the devices of the system may performcommunication pulse ELRT tests. These communication pulse ELRT tests mayestablish an energy level of delivered communication pulses such thatthe energy level of the delivered communication pulses received at thereceiving device may be close to, but still above, the MCRT of thereceiving device.

In some additional or alternative examples, a device may employ amaximum energy threshold test. A maximum energy threshold test (MELT)may establish a maximum energy level of communication pulses that adevice may be configured to deliver. The maximum energy threshold may bean energy level threshold where delivering communication pulses withenergy levels above the maximum energy threshold may cause unwantedstimulation of the patient (e.g. capture of the heart, stimulation ofmuscles, stimulation of nerves, etc.). As with the other tests, a devicemay periodically perform a MELT test. Typical periods between performinga MELT test may include once a day, once a week, once a month, or anyother suitable period of time. In other examples, a device may perform aMELT test based on trigger events, for example upon detection of athreshold amount of cardiac capture events caused by deliveredcommunication pulses, after delivery of a defibrillation pulse, afterdelivery of ATP therapy, after a detected threshold change in the amountof energy currently stored in an energy storage module, or after adetected threshold change in temperature. For instance, a devicedelivering communication pulses may monitor for whether the deliveredcommunication pulses capture the heart. Upon detection of a thresholdamount of capture events, the device may perform a MELT test. In otherexamples, other devices may monitor for capture events and communicate atrigger to the device that delivered the communication pulses afterdetecting a threshold amount of capture events. In addition to theforegoing, and in some cases, a trigger event may include other eventssuch as a change in a device parameter (e.g. pacing rate), a change in apatients activity (change in hemodynamic demand), a change in a patientsposture, a detected patient event (e.g. defibrillation shock), a changein a communication parameter (e.g. frequency). In some cases, a devicemay perform a MELT test at implant, periodically and/or upon triggerevents.

In some examples, one or more of the devices may monitor for an evokedresponse in order to determine whether the heart was captured by one ormore communication pulses. Alternatively, or in addition, one or more ofthe devices may monitor for a loss of, or delayed, intrinsic event.Other methods for determining whether the heart was captured can befound in U.S. Provisional Patent Application No. 62/034,494, filed onAug. 7, 2014 (BSC File No.: 14-0109PV01, STW: 1001.3572100), entitled“Medical Device Systems and Methods with Multiple Communication Modes,”the entirety of which is incorporated herein by reference. If, based onthe disclosed one or more methods, the device determines thatcommunication pulses delivered by the device captured the heart, thenthe device may perform a MELT test.

While capture of the heart is used here as an example of unwantedstimulation, it is contemplated that unwanted stimulation may includeany suitable unwanted stimulation event, such as unwanted nerve ormuscle stimulation. For example, an accelerometer or the like in LCP 402may be used to detect movement of the diaphragm or unwanted hiccuppingcaused by unwanted stimulation of the phrenic nerve by communicationpulses. In such examples, movement of the accelerometer in a time windowafter delivering a communication pulse may be indicative of unwantedstimulation—as the unwanted nerve or muscle stimulation may cause LCP402, and accordingly the accelerometer, to move.

In performing a MELT test, a device, such as LCP 402 or the S-ICD, maydetermine multiple combinations of parameters for pulses (e.g.communication pulses or test pulses) which result in capture of theheart, thereby determining multiple capture thresholds for the heart.Using the determined multiple combinations of parameters, LCP 402 maydetermine a curve or function representative of combinations ofparameters which resulted in capture of the heart, for example by usingone or more regression techniques. Continuing the examples described inFIGS. 6-9, LCP 402 may use conducted pulses, where the energy level ofthe pulses may be related to the voltage amplitude and the pulse widthparameters of the pulses. FIG. 13, then, is a graph of pulse amplitudevs. pulse width in millivolts and milliseconds, and includes anillustrative example of what such a curve or function may look like.Curve 1302 represents combinations of parameters of pulses which mayresult in capture of the heart—e.g. curve 1302 may represent a capturethreshold curve. Curve 1302 additionally represents a dividing linebetween combinations of parameters of conducted pulses which, whendelivered to tissues of a patient, would result in capture of thepatient's heart and those that would not result in capture of thepatient's heart. For instance, any combinations of pulse amplitudes andpulse widths that lie on curve 1302 or above and to the right of curve1302 would result in capture. Any combinations of pulse amplitudes andpulse widths that lie below and to the left of curve 1302 would notresult in capture. This region is defined as safe zone 1310.

In some examples, LCP 402 may determine a shifted curve related to curve1302 by a safety margin. The shifted curve is represented by curve 1308.In such examples, safe zone 1310 may be the combinations of pulseamplitudes and pulse widths that lie below and to the left of shiftedcurve 1308. The amount LCP 402 shifts curve 1302 is represented bysafety margin 1306. Safety margin 1306 may represent an amount such thatif curve 1302 changes as a function of time or other factors, curve 1302will not, or is statistically unlikely to, drift below and to the leftof curve 1308. Curve 1308 may be considered the maximum energy thresholdfor LCP 402. LCP 402 may be configured to not deliver conductedcommunication pulses with combinations of parameters that lie on curve1308 or above and to the right of curve 1308. In some examples, curve1302 and/or curve 1308 may be considered unwanted stimulationthresholds.

During a MELT test, LCP 402 may deliver communication pulses to tissueof the patient that cause capture of the heart. Accordingly, in someMELT tests during periods where LCP 402 is currently providingelectrical stimulation therapy, LCP 402 may deliver communication pulsesin lieu of pacing pulses. If LCP 402 determines that a deliveredcommunication pulse did not cause capture of the heart, for example bydetecting a lack of an evoked response in a time period succeeding thedelivered communication pulse, LCP 402 may then deliver a safety pacingpulse. The safety pacing pulse, which may be similar to a pacing pulse,is designed to ensure capture of the heart occurs. In this manner, LCP402 may save energy by employing communication pulses to capture theheart of the patient and only employing additional pulses, e.g. safetypacing pulses, if the delivered communication pulses failed to capturethe heart, rather than delivering both communication pulses and pacingpulses. Additionally, by only employing safety communication pulses, LCP402 may avoid an issue with causing multiple captures of the heart fromboth the communication pulses and the pacing pulses.

In examples where LCP 402 determines a maximum energy threshold, LCP 402may additionally compare the maximum energy threshold to the energylevels determined based on communication pulse energy level reductiontests. For instance, in the example of FIG. 12, LCP 402 determinedvalues of one or more voltage amplitude parameters and/or values of oneor more pulse width parameters of communication pulses that LCP 402 maydeliver to tissue of the patient when communicating with other devices.If LCP 402 determines that one or more of the determined combinations ofparameters for the communication pulses lie on or is above and to theright of curve 1308, LCP 402 may take one or more actions. For instance,LCP 402 may cease delivering communication pulses for communication withany device for which the associated one or more voltage amplitudeparameters and/or one or more pulse width parameters lie on or above andto the right of curve 1308. In other examples, LCP 402 may enter asafety communication mode, such as described in U.S. Provisional PatentApplication No. 62/034,494, filed on Aug. 7, 2014 (BSC File No.:14-0109PV01, STW: 1001.3572100), entitled “Medical Device Systems andMethods with Multiple Communication Modes”, which may limit thecommunication functionality of LCP 402. When in the normal communicationmode, LCP 402 may be configured to deliver communication pulses withinone or more first communication windows during each cardiac cycle. Inthe safety communication mode, LCP 402 may be configured to delivercommunication pulses within one or more second communication windowsduring each cardiac cycle. The one or more second communication windowsmay be shorter than the one or more first communication windows.Alternatively, or additionally, the one or more second communicationwindows may occur at different times within a cardiac cycle than the oneor more first communication windows.

Additionally, or alternatively, any the above described examples mayinclude performing the disclosed tests for each available vector of thedevice. In some examples, one or more devices of a system may be able todeliver and/or receive communication pulses via different vectors, wherea vector is a combination of at least two electrodes. A vector maycomprise two of any of combination of implanted, percutaneous, ortranscutaneous electrodes that are found on a device. For instance, adevice may include more than two electrodes and may accordingly deliverand/or receive communication pulses via different combinations of theelectrodes. Each available receiving vector for a device may receivedifferent levels of noise or other signals. Additionally, the energylevel of a communication pulse or the level of attenuation of thecommunication pulse may be affected by the specific vector via which adevice delivers the communication pulse. Accordingly, in some examples adevice may perform an MCRT test, a ELR test, or a MELT test for eachavailable vector of the device. The device may then select anappropriate receiving vector and an appropriate delivering vector. Theappropriate receiving vector may be the vector with the lowest MCRTvalue. The appropriate delivering vector may be the vector for which thedevice determined communication pulses for future communication use thathad the lowest energy level out of all the determined communicationpulses for all of the other vectors. In some ELR test examples,selecting a receiving vector and/or a delivering vector may occurinstead of adjusting any of the parameters of the communication pulses.

FIG. 14 is a flow diagram of an illustrative method that may beimplemented by an implantable medical device, such as shown in FIGS. 1and 2, or a medical device system such as shown in FIGS. 4 and 5.Although the method of FIG. 14 will be described with respect to LCP 100and an S-ICD, the illustrative method of FIG. 14 may be performed usingany suitable medical devices or medical device systems. FIG. 14 showsone illustrative MELT test.

According to the method depicted in FIG. 14, a medical device may beimplanted within a patient, such as if the medical device is an LCP,ICP, an ICD, an S-ICD, or may be disposed in proximity to the patient,such as if the medical device is an external medical device. The medicaldevice may be configured to deliver a plurality of communication pulsesto tissue of the patient, where each communication pulse includes anamount of energy, and for each delivered communication pulse, it may bedetermined whether the delivered communication pulse produces anunwanted stimulation of the patient, as shown at 1402. In some cases,the medical device that delivered the communication pulses may determinewhether the delivered communication pulse produces an unwantedstimulation of the patient. In other cases, another medical device, suchas the receiving medical device or some other medical device (e.g.accelerometer, acoustic sensor, etc.) may determine whether thedelivered communication pulse produces an unwanted stimulation of thepatient. The medical device may change the amount of energy of theplurality of communication pulses over time so that an amount of energythat corresponds to an unwanted stimulation threshold for thecommunication pulses can be identified, as shown at 1404. The medicaldevice may then set a maximum energy value for subsequent communicationpulses that is below the identified unwanted stimulation threshold, asshown at 1406.

FIG. 15 is a flow diagram of an illustrative method that may beimplemented by an implantable medical device, such as shown in FIGS. 1and 2, or a medical device system such as shown in FIGS. 4 and 5.Although the method of FIG. 15 will be described with respect to LCP 100and an S-ICD, the illustrative method of FIG. 15 may be performed usingany suitable medical devices or medical device systems.

According to the illustrative method depicted in FIG. 15, a firstmedical device may be implanted within a patient, such as if the firstmedical device is an ICP, an ICD, an S-ICD, or may be disposed inproximity to the patient, such as if the first medical device is anexternal medical device. The first medical device may be part of amedical device system along with a second medical device, such as LCP100. In such a medical device system, a first medical device may deliverone or more first communication pulses where each first communicationpulse includes a first amount of energy, as shown at 1502. The secondmedical device may then determine a number of the one or more firstcommunication pulses received by the second medical device, as shown at1504. The first medical device may then deliver one or more secondcommunication pulses where each second communication pulse includes asecond amount of energy, as shown at 1506. The second medical device maythen determine a number of the one or more second communication pulsesreceived by the second medical device, as shown at 1508. Finally, thefirst medical device may adjust a minimum communication pulse energy forwhen the first medical device subsequently communicates with the secondmedical device based on the number of the one or more firstcommunication pulses received by the second medical device and thenumber of the one or more second communication pulses received by thesecond medical device, as shown at 1510. Of course in other examples,LCP 100 may be the first medical device, and the second medical devicemay be any of an ICP, an ICD, an S-ICD, or an external medical device.

FIG. 16 is a flow diagram of an illustrative method that may beimplemented by an implantable medical device, such as shown in FIGS. 1and 2, or a medical device system such as shown in FIGS. 4 and 5.Although the method of FIG. 16 will be described with respect to LCP 100and an S-ICD, the illustrative method of FIG. 16 may be performed usingany suitable medical devices or medical device systems.

According to the illustrative method depicted in FIG. 16, a medicaldevice may be implanted within a patient, such as if the first medicaldevice is an LCP, ICP, an ICD, an S-ICD, or may be disposed in proximityto the patient, such as if the first medical device is an externalmedical device. The medical device may operate to determine a minimumreceive threshold for use when receiving communication signals fromanother device. For example, the medical device may set the minimumcommunication receive threshold to a first level, as shown at 1602. Themedical device may then determine a number of detected communicationsignals with the minimum communication receive threshold at the firstlevel, as shown at 1604. The communication signals may, for example, bedelivered by another device to tissue of the patient and for receptionby the medical device. The other medical device may be, for example, anLCP, ICP, ICD, S-ICD, or an external medical device. The medical devicemay then change the minimum communication receive threshold to a secondlevel, wherein the second level is different than the first level, asshown at 1606. Then, the medical device may determine a number ofdetected communication signals with the minimum communication receivethreshold at the second level, as shown at 1608. Again, thecommunication signals may be delivered by the other medical device. Themedical device then determines a value for the minimum communicationreceive threshold based on the determined number of detectedcommunication signals, as shown at 1610. Finally, the medical device mayset the minimum communication receive threshold to the determined value,as shown at 1612, and use the set minimum communication receivethreshold during subsequent communication between the medical device andthe other medical device, as shown at 1614.

Those skilled in the art will recognize that the present disclosure maybe manifested in a variety of forms other than the specific examplesdescribed and contemplated herein. For instance, as described herein,various examples include one or more modules described as performingvarious functions. However, other examples may include additionalmodules that split the described functions up over more modules thanthat described herein. Additionally, other examples may consolidate thedescribed functions into fewer modules. Accordingly, departure in formand detail may be made without departing from the scope and spirit ofthe present disclosure as described in the appended claims.

What is claimed:
 1. A method for setting an energy level forcommunication pulses of a medical device, the method comprising:delivering a plurality of pulses to tissue of a patient, where eachpulse includes an amount of energy, and for each delivered pulse,determining whether the delivered pulse produces an unwanted stimulationof the patient; changing the amount of energy of the plurality of pulsesover time so as to identify an amount of energy that corresponds to anunwanted stimulation threshold for the pulses; and setting a maximumenergy value for communication pulses that is below the unwantedstimulation threshold.
 2. The method of claim 1, wherein the maximumenergy value is set a predetermined safety margin below the unwantedstimulation threshold.
 3. The method of claim 1, wherein the unwantedstimulation is a capture of a heart of the patient.
 4. The method ofclaim 3, wherein delivering a plurality of pulses to tissue of a patientcomprises delivering a pulse in lieu of a pacing pulse, and delivering asafety pacing pulse if the pulse did not capture the heart.
 5. Themethod of claim 1, wherein the unwanted stimulation is a stimulation ofa nerve of the patient.
 6. The method of claim 1, wherein the unwantedstimulation is a stimulation of a muscle of the patient.
 7. The methodof claim 1, wherein the amount of energy of each pulse is defined atleast in part by an amplitude, a pulse width, a morphology, or thespecific vector via which the pulse is delivered.
 8. The method of claim1, further comprising repeating the delivering, changing and settingsteps from time to time.
 9. The method of claim 1, further comprisingrepeating the delivering, changing and setting steps in response to atrigger event.
 10. A medical device comprising: a communication moduleconfigured to deliver a plurality of pulses to tissue of a patient,where each pulse comprises an amount of energy; a control moduleoperatively coupled to the communication module, the control moduleconfigured to: for each delivered pulse, determine whether the deliveredpulse produces an unwanted stimulation of the patient; change the amountof energy of the plurality of pulses over time so as to identify anamount of energy that corresponds to an unwanted stimulation thresholdfor the pulses; set a maximum energy value for communication pulses thatis below the unwanted stimulation threshold; and deliver communicationpulses below the maximum energy value during communication with anotherdevice.
 11. The medical device of claim 10, wherein the maximum energyvalue is set a predetermined safety margin below the unwantedstimulation threshold.
 12. A method for adjusting a communicationprotocol between a plurality of medical devices, the method comprisingwith a first medical device, delivering one or more first pulses whereeach first pulse includes a first amount of energy; determining a numberof the one or more first pulses received by a second medical device;with the first medical device, delivering one or more second pulseswhere each second pulse includes a second amount of energy; determininga number of the one or more second pulses received by the second medicaldevice; and adjusting a minimum communication pulse energy for the firstmedical device when communicating with the second medical device basedon the number of the one or more first pulses received by the secondmedical device and the number of the one or more second pulses receivedby the second medical device.
 13. The method of claim 12, wherein theamount of energy of each pulse is defined at least in part by anamplitude and a pulse width.
 14. The method of claim 13, whereinadjusting the minimum communication pulse energy for the first medicaldevice when communicating with the second medical device comprisesadjusting the pulse width of each communication pulse used tocommunicate with the second medical device.
 15. The method of claim 13,wherein adjusting the minimum communication pulse energy for the firstmedical device when communicating with the second medical devicecomprises adjusting the amplitude of each communication pulse used tocommunicate with the second medical device.
 16. The method of claim 13,wherein adjusting the minimum communication pulse energy for the firstmedical device when communicating with the second medical devicecomprises adjusting the pulse width and the amplitude of eachcommunication pulse used to communicate with the second medical device.17. The method of claim 12, wherein adjusting the minimum communicationpulse energy for the first medical device when communicating with thesecond medical device based on the number of the one or more firstpulses received by the second medical device and the number of the oneor more second pulses received by the second medical device comprisessetting the minimum communication pulse energy for the first medicaldevice when communicating with the second medical device to the amountof energy of the one or more first and second pulses with the lowestacceptable number of pulses received by the second medical device. 18.The method of claim 17, further comprising adding a predetermined safetymargin to the minimum communication pulse energy.
 19. The method ofclaim 12, further comprising determining whether the adjusted minimumcommunication pulse energy overlaps a maximum energy threshold.
 20. Themethod of claim 19, further comprising, after determining the adjustedminimum communication pulse energy overlaps the maximum energythreshold, by the first medical device, entering a safe communicationmode.